Question

我正试图在本周获得星期一的日期。这接近正确吗？

Dim MondayOfCurrentWeek As Date = Date.Today - Date.Today.DayOfWeek + 1

据我了解，AyOfWeek索引是：

1 = Monday
2 = Tuesday
3 = Wednesday
4 = Thursday
5 = Friday
6 = Saturday
0 = Sunday

因此，如果例如“今日约会”是星期四，我会得到：

Dim MondayOfCurrentWeek As Date = Date - 4 + 1

等于

Date - 3

对我来说似乎是正确的。

还是我完全离开？

Answer 1

一种非常简单的替代方法，虽然可能没有那么高效，但可以避免任何基于算术的错误：

Dim monday As Date = Date.Today
While (monday.DayOfWeek <> DayOfWeek.Monday)
    monday = monday.AddDays(-1)
End While

这可以很容易地扩展到一个函数来处理一周中的任何一天。除非这是一个非常大量的代码，否则性能会很好。

Answer 2

这应该做你想要的。它从提供的日期开始查找上一个星期一。没有循环因此会很快并且不依赖于枚举值来进行算术调整，所以如果枚举值发生变化则不会中断：

Public Shared Function PreviousMonday(ByVal dateValue As DateTime) As DateTime
    Dim dayOffset As Integer
    Select Case dateValue.DayOfWeek
        Case DayOfWeek.Sunday : dayOffset = 6
        Case DayOfWeek.Monday : dayOffset = 0
        Case DayOfWeek.Tuesday : dayOffset = 1
        Case DayOfWeek.Wednesday : dayOffset = 2
        Case DayOfWeek.Thursday : dayOffset = 3
        Case DayOfWeek.Friday : dayOffset = 4
        Case DayOfWeek.Saturday : dayOffset = 5
    End Select

    Return dateValue.AddDays(-1 * dayOffset)
End Function

Answer 3

如果您要查找上周的周一至周日范围，则可以使用这些功能（Matt Wilko回答的修改版）来获取它们。

Public Shared Function PreviousMonday(ByVal dateValue As Date) As Date
Dim dayOffset As Integer
Select Case dateValue.DayOfWeek
    Case DayOfWeek.Sunday : dayOffset = -13
    Case DayOfWeek.Monday : dayOffset = -7
    Case DayOfWeek.Tuesday : dayOffset = -8
    Case DayOfWeek.Wednesday : dayOffset = -9
    Case DayOfWeek.Thursday : dayOffset = -10
    Case DayOfWeek.Friday : dayOffset = -11
    Case DayOfWeek.Saturday : dayOffset = -12
End Select

Return dateValue.AddDays(dayOffset)
End Function

Public Shared Function PreviousSunday(ByVal dateValue As Date) As Date
Dim dayOffset As Integer
Select Case dateValue.DayOfWeek
    Case DayOfWeek.Sunday : dayOffset = -7
    Case DayOfWeek.Monday : dayOffset = -1
    Case DayOfWeek.Tuesday : dayOffset = -2
    Case DayOfWeek.Wednesday : dayOffset = -3
    Case DayOfWeek.Thursday : dayOffset = -4
    Case DayOfWeek.Friday : dayOffset = -5
    Case DayOfWeek.Saturday : dayOffset = -6
End Select

Return dateValue.AddDays(dayOffset)
End Function

Answer 4

var now = DateTime.Now; //17.09.2020 19:15:49
int dayInWeek = (int)now.DayOfWeek; //4
var previousMonday = now.AddDays(-(((dayInWeek + 6) % 7) + 7)); //-10
var previousSunday= previousMonday.AddDays(6); //-4
        
Console.WriteLine(previousMonday); //07.09.2020 19:15:49
Console.WriteLine(previousSunday); //13.09.2020 19:15:49

获取上周一的日期

4 个答案: